It is known that the manufacture of prestressed concrete poles involves the casting and hardening of concrete in molds with special requirements for the operations of positioning, stressing and loosening the mold. To date, there have been many commercial articles made from prestressed concrete materials. These articles include tubular pipes, beams, support columns, and poles, which may be reinforced by steel strands in the concrete or by rods, bars, and/or tubes for reinforcement located in the concrete. A large number of prestressed concrete articles have been manufactured and it is always desirable to provide means which makes the manufacturing of these articles less expensive as well as easier to accomplish.
Prestressed concrete lamp poles are cast in a mold. The empty mold is assembled, and in order to prestress a concrete pole, an axial compressive load is placed on the mold. The axial load is transmitted through the mold by prestressing strands which extend through the mold and are attached at either end of the mold. After prestressing, the mold is pumped full of concrete and rotated to centrifugally consolidate the concrete. Once the mold is full, it is generally conveyed through a heated chamber to accelerate the curing of the concrete. The prestressing load is then ready to be transferred from the mold to the pole and the mold can be removed from the finished product.
Typical molds used to cast concrete poles are solid steel molds. Depending upon the intricacy or the ornamentality of the pole to be cast, the mold is composed of separate segments corresponding to each distinct pattern located on the pole. Solid steel molds are composed of two or more pieces in which the pattern to be cast is machined into the interior surface of the mold pieces such that when the pieces are joined together a hollow cavity exists corresponding to the pattern of the pole.
A number of patterns can be incorporated into a single pole, however, it is also common for a single pattern to dominate a pole structure. A very popular pattern for a concrete lamp pole is a fluted pattern. Generally, a fluted pattern dominates the overall pattern of a lamp pole.
There are two problems associated with solid steel molds used to cast a fluted pattern. First, it is very expensive to machine flutes into the mold, and secondly, since a flute pattern can extend many feet along the length of the pole, a solid steel mold is very heavy. Because the mold is so heavy a substantial amount of time and equipment is required to assemble the mold.
Many concrete pole molds are made of segments to be interchangeable so that the designs of the poles can be varied by changing one or more of the segments without having to reconstruct the entire mold. However, since a fluted mold segment is so heavy, changing that segment requires a longer amount of time to accomplish the task.
A third problem associated with segmented solid steel molds is maintaining concentricity when arranging the mold segments. This problem is particularly evident at undercut portions of a pole design. A lack of concentricity can create surface irregularities in a cast pole. To eliminate this problem many pole designs simply forego any undercut portions.
Thus, there exists a long felt need for a new and improved fluted concrete pole mold which is inexpensive to manufacture, lightweight, and provides a means for maintaining concentricity as the mold is assembled, even when the mold contains segments for undercut portions of the pole.